(a) Field of the Invention
The present invention relates to a display device and a driving method thereof, and more particularly, to an organic light emitting diode display and a driving method thereof.
(b) Description of Related Art
In general, in active type flat display devices, a plurality of pixels are arrayed in a matrix, and intensity of light of the pixels is controlled according to given brightness information so that an image is displayed. The organic light emitting diode (OLED) display is a display device which electrically excites phosphorous organic materials to display an image. As a self-emitting display device with low power consumption, a wide viewing angle, and a high response speed, the OLED display can easily display a high quality moving image.
The OLED display includes organic light emitting devices (OLEDs) and thin film transistors (TFTs) which drive the OLEDs. The TFTs are classified into polysilicon TFTs and amorphous silicon TFTs according to types of active layers.
Since amorphous silicon can be deposited at a low temperature to form a thin film, the amorphous silicon is mainly used for a semiconductor layer of a switching element of a display device that includes a glass substrate having a low melting point. However, due to low electron mobility of the amorphous silicon TFT, it is difficult to obtain a wide-area display device by using the amorphous silicon TFT. In addition, as a direct current is continuously supplied to a control terminal of the amorphous silicon TFT, a threshold voltage of the TFT may be shifted, so that the TFT may deteriorate. For the reason, the lifetime of the OLED display may be greatly reduced.
Therefore, a polysilicon TFT having high electron mobility, a good high-frequency operating characteristic, and a low leakage current is required. Particularly, a low temperature polysilicon (LTPS) backplane may increase the lifetime of the OLED display. However, marks of laser shots involved in laser crystallization may cause a deviation in the threshold voltage of the driving transistors in one panel, so that screen uniformity may deteriorate.